Acquisitions lineitem update barcode silent fail with missing catalog item record

v.3.6.4, using on-order ACQ holdings records and shelf-ready item holdings overlay (and vendor processing)

Situation:

1 - A shelf-ready item arrived at the library and was scanned in checkin to be put into circulation. The item barcode, which should have been added with the holdings overlay, returned "Item not found".
2 - The staff person opened the associated PO, located the lineitem record with on-order copy information.
3 - They clicked lineitem actions > update barcodes which opened the holdings editor.
4 - They scanned the item barcode and updated the copy record fields, clicked save and exit.
5 - On scanning the item barcode again, it still returned "item not found".

On further in investigation, opening the catalog from the lineitem link, there was no on-order, or any other, copy record.

Presumably the on-order record was accidentally deleted, or was not uploaded to the catalog.

This was duplicated by locating a line item with an on-order item in the catalog, deleting the item from the catalog, then returning to the PO and attempting to update the barcode.

One would expect an error/failure message.